Reproductive Factors but Not Hormonal Factors Associated with Thyroid Cancer Risk: A Systematic Review and Meta-Analysis

Table 2

Summary results for the association between hormonal and reproductive factors and thyroid cancer risk.

Comparisons	^aRR	^b95% CI	value	Tests for heterogeneity
				(%)
All
Oral contraceptive	0.94	0.85–1.04	0.215	36.0	0.095
Hormone replacement therapy	1.04	0.91–1.19	0.527	0	0.520
Age at menarche	1.08	0.97–1.19	0.142	0	0.486
Parity	1.10	0.94–1.28	0.234	61.2	<0.001
Age at first birth	1.07	0.95–2.20	0.255	14.8	0.281
Menopausal status	0.96	0.79–1.18	0.727	4.9	0.394
Age at menopause	1.24	1.00–1.53	0.049	26.4	0.201
Duration of breast feeding	0.84	0.65–1.08	0.178	38.3	0.150
Breast feeding	0.84	0.69–1.02	0.080	4.9	0.368
Cohort studies
Oral contraceptive	0.96	0.86–1.07	0.448	39.5	0.104
Hormone replacement therapy	1.05	0.91–1.20	0.513	0	0.439
Age at menarche	1.01	0.90–1.14	0.808	16.1	0.299
Parity	1.00	0.78–1.28	0.993	70.6	<0.001
Age at first birth	1.04	0.92–1.18	0.530	0	0.571
Menopausal status	0.90	0.71–1.15	0.418	26.6	0.252
Age at menopause	1.3	1.04–1.63	0.022	2.5	0.400
Duration of breast feeding	0.70	0.51–0.95	0.021	0	0.661
Breast feeding	0.82	0.66–1.02	0.078	0	0.442
PCC
Oral contraceptive	0.89	0.73–1.08	0.240	41.0	0.166
Hormone replacement therapy	1.01	0.68–1.50	0.962	6.0	0.363
Age at menarche	1.28	1.04–1.57	0.960	0	0.937
Parity	1.00	0.93–1.07	0.960	21.6	0.258
Age at first birth	1.35	0.97–1.88	0.072	42.3	0.123
Menopausal status	1.10	0.78–1.57	0.577	0	0.481
Age at menopause	0.82	0.43–1.56	0.554	44.0	0.147
Duration of breast feeding	1.24	0.80–1.93	0.332	28.2	0.248
Breast feeding	0.92	0.60–1.41	0.699	57.6	0.125
HCC
Parity	2.30	1.31–4.04	0.004	0	0.787

^aRR: relative risk; ^b95% CI: 95% confidence interval; ^cP: the value of for pooled analysis; ^dP: the value of for heterogeneity analysis.